Throttle valves in carburetors for small internal combustion engines adjust the air-fuel mixture supplied to the engine. The throttle valves are commonly supported for rotation in a mixing passage of the carburetor to selectively open and close the mixing passage. In additional to rotational movement, throttle valves are known to be axially moveable to displace a needle valve within a fuel nozzle to regulate the rate of fuel flow into the mixing passage.
The axial movement of the throttle valve is controlled by a cam assembly including a cam follower carried by the carburetor and a cam provided on a lever coupled to the throttle valve for mating engagement with the cam. As the throttle valve lever is rotated, the throttle valve rotates about its longitudinal axis to regulate the flow of air through the mixing passage and moves axially to regulate the flow of liquid fuel into the mixing passage.
As a result of the cam assembly being disposed outside of the carburetor body, dust and debris can accumulate between the cam and the cam follower. As such, the movement of the throttle valve is adversely affected, thereby resulting in inefficient, unsteaady or undesirable engine performance. Further, the accumulation of contamination, such as dust, can reduce the life of the throttle valve assembly and related components.